Liquid/solid separator and method

ABSTRACT

A liquid/solid separator system mounted on a mobile cart and connected to a process tank for reducing the rate at which fluids are consumed in manufacturing processes. The system may include automation and also may include a shear-stepped screen including tilted wire wedge wires arranged at varying cant angles. The system may include a fine screen basket received in a settling box.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 11/291,049, filed Nov. 29, 2005, entitled “LIQUID/SOLID SEPARATORAND METHOD”, now U.S. Pat. No. 7,303,672, which is a continuation ofU.S. patent application Ser. No. 10/412,899, filed Apr. 14, 2003,entitled “LIQUID/SOLID SEPARATOR AND METHOD”, now U.S. Pat. No.6,986,849, both of which are incorporated herein by this reference.

FIELD OF THE INVENTION

This invention relates to a liquid/solid separator and method orprocess.

BACKGROUND OF THE INVENTION

Many industries consume large volumes of fluids (predominately water),chemical additives and reagents in manufacturing products. The fluidsare used primarily in rinsing, cooling and treatment operations toachieve desired product quality and cleanliness. In industry,manufactured products are often immersion rinsed and/or sprayed severaltimes along an assembly line via immersion tanks and/or high-pressurespray washer conveyors. Excess solid debris loosely adhering to newlymanufactured or remanufactured products is washed off inrinsing/spraying processes and accumulates in short order in reservoirsof immersion and spray waters, which degrades the cleansing ability ofthe fluid, leaving it ineffective in achieving desired product quality.Depending on the manufacturing process, the entire volume (typicallybetween 400 to 2000 gal.) of fluid in an immersion tank or recirculantspray washer conveyor may be discharged daily to waste and refreshedwith new fluid and chemical additive to restore effective cleansingability. A significant cost burden is associated with up-frontpurchasing, inventorying and administration in re-supplying fresh fluidsand additives, which is furthered in properly treating (physically,chemically & biologically) used fluids before discharging to theenvironment for natural recycling. Therefore, both business andenvironmental perspectives share a common desire, which is tosignificantly reduce the rate at which fluids are consumed inmanufacturing processes.

At present, conventional approaches to solving and/or mitigating theaforementioned problem are fraught with inefficiencies that include: 1)high initial capital equipment cost; 2) difficulty in installation andmobilization of equipment; 3) difficulty in understanding andcontrolling operation; 4) requirements for formal training to operateand maintain; 5) difficulty in troubleshooting; 6) high frequency wearparts and many moving parts; 7) requirements for specialty tools inoperating and maintaining; 8) large, heavy and extensive (largefootprint); 9) high incremental cost in replacing consumable filtrationmedia; 10) strict physical property requirements of accumulating solidsin specific gravity, size, shape, consistency and character; 11) highassociated maintenance time and cost; 12) pressure- and flow-sensitive;13) limited scope by relying largely on a single principal of operation;14) low efficiency; 15) undesirable interruption of main process whenmaintaining; 16) frequent and voluminous discharge and flush volumesrequired during automatic cleaning cycles; 17) largely non-automatic incleaning internal elements; 18) high associated energy cost; 19)difficulty in accessing and maintaining internal elements; 20) frequentmalfunction; 21) frequent obstruction of critical elements; 22)auxiliary power requirements and controls in initiating auto-cleaningmodes; 23) sharing of filtration equipment between reservoir tanks isprohibitive due to conventional design mindset around a necessarilypermanent configuration; 24) filtration equipment typically does notcome fully packaged, requiring integration of ancillary equipment,controls and instrumentation; 25) replacement of internal elements indetermining ideal media pore sizes is expensive and time-consuming; 26)units are easily tampered with; 27) high shipping and handling costs onweight and volume basis; 28) degree of influence in removing solids fromfluids is not appreciable (rate of fluid contamination is appreciablygreater than rate of solids removal); 29) disassembly is time-consuming,difficult and potentially unsafe; 30) low return on investmenttranslating into long payback periods; 31) operational results selfishlyfavoring either business perspective or environmental perspective; and32) that problem is not truly solved, rather, it is transferred.

SUMMARY OF THE INVENTION

One embodiment of the invention involves a unique design thatsignificantly reduces the consumption rate of fluids used in industrialprocesses while largely optimizing, balancing and mitigating theaforementioned operational- and maintenance-related efficiencies. Thedesign integrates four (4) distinct separation elements that areoptimally arranged to achieve desired results:

-   -   I. Coanda Tilted Wire Wedge-wire Coarse Screen (Primary        Separation Element)    -   II. Woven-wire Mesh Fine Screen (Secondary Separation Element)    -   III. Settling Box (Tertiary Separation Element)    -   IV. Magnets (Quaternary Separation Element)

Another embodiment of the invention is a liquid/solid separator systemincluding a first screen arranged at an angle to the horizontal andhaving an upper end and a lower end. There is also provided a first linefor moving a solid-containing fluid above the upper end of said screento cause the solid-containing fluid to move down and across the screenunder the influence of gravity. A settling box is positioned below thelower end of the first screen. A strainer basket is received within thesettling box in spaced relation to the settling box.

Still another embodiment of the invention is a process for separatingsolids from liquids which involves providing a process tank whichcontains a solid-containing liquid. A first filter screen is providedarranged at an angle to the horizontal and having an upper end and alower end. An active return line is positioned below the first screen toreceive a liquid which flows through the screen and returns it to theprocess tank. A discharge chute is provided at the lower end of thefirst filter screen for receiving and conveying liquid and solids thatdo not pass through the first screen. A second filter screen which isfiner in pore size than the first filter screen is provided and receivesthe liquid and solids exiting from the discharge chute. A settling boxis provided, receiving the second filter screen. The solid-containingliquid flows from the process tank to the first filter screen toseparate solids from the solid-containing liquid and then the flowthrough the active return line is shut off to rinse the first filterscreen and cause solids thereon to pass into the discharge chute.

Another embodiment of the invention is a filter screen for separatingsolids and liquids which includes a series of wires and a series of ribshaving the wires fixed thereto in a pattern wherein the wires areparallel to each other. Each wire of the series of wires has a crosssection which is a triangle with two sides of the triangle forming avertex which is the point at which the wire is fixed to the ribs. Theremaining side of the triangle is tilted at an angle to the ribs. Thescreen has an upper end and also a lower end and the tilt angle isgreater for the wires at the upper end than it is for the wires at thelower end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the liquid solid separator of thepresent invention with certain elements removed to show internalconstruction.

FIG. 2 is a side elevation view of the liquid solid separator of thepresent invention showing it in normal operation mode.

FIG. 3 is a view similar to FIG. 2 showing the separator in maintenancemode.

FIG. 4 is a view similar to FIGS. 2 and 3 showing the separator furtherdisassembled in maintenance mode.

FIG. 5 is a rear elevation view.

FIG. 6 is a fragmentary enlarged section of the coarse filter screentaken along line 6-6 of FIG. 5.

FIG. 7 is a perspective view of the coarse filter screen looking at itfrom above.

FIG. 8 is a perspective view of the fine filter screen.

FIG. 9 is a perspective view of a stand/cart upon which the elements ofthe separator are mounted.

FIG. 10 is a perspective detail view of a separation pan forming a partof the separator.

FIG. 11 is a view similar to FIG. 6 of an alternative embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated devices, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

Referring to the drawings and particularly to FIG. 2, there isillustrated an apparatus 10 that includes four separation elements. Theprimary separation element is a tilted wire wedge-wire coarse screen 11.The secondary separation element is a woven wire mesh fine screen 12.The tertiary separation element is a settling box 15 and the quaternaryseparation element is magnets 16 and 17. These four elements operate infour modes of operation: 1) normal operation mode, 2) screen rinse mode,3) maintenance mode and 4) tank refresh mode.

The apparatus 10 includes seven major assemblies that are connected byappropriate hydraulic connections. Four of those major assemblies arethe primary separation assembly 20 which includes the coarse screen 11,the secondary separation assembly which includes the fine screen 12 andthe settling box 15, the tertiary separation assembly which is thesediment basin or process tank 21 and the quaternary separation assemblywhich includes the magnets 16 and 17. The remaining major assemblies arethe recirculating pump assembly 22, the pump/screen rinse controllerassembly 25 and the rinse valve assembly 26.

The recirculating pump assembly 22 includes a self-priming trash pump 23which is coupled to the process tank 21 through a pump suction line 30and a sparger return line 31. Various kinds of pumps may be used inplace of the trash pump 23 and some embodiments of the invention may notinclude any pump (i.e., where sufficient elevation head is supplied by aprocess stream). However, a trash pump 23 is preferred, particularly ifthe solids involved include relatively large items. In one preferredembodiment of the invention, the trash pump 23 is a product of MP Pump,Inc. of Tecumseh Products Company of Detroit, Mich. The trash pump 23 isalso coupled by the pump discharge line 24 to the head compartment 32 ofa separation pan 35 which houses the coarse screen 11. The pumpdischarge line splits into two lines, 24A and 24B, as shown in FIGS. 1and 5. The lower end of the separation pan has mounted thereon aliquid/solid discharge chute 36. Also connected to the lower end of theseparation pan is an active return line 37 which returns filtered fluidback to the process tank 21. The active return line is coupled to theseparation pan at a location directly below the screen 11 and at alocation where it receives liquid passing through the screen onto theseparation pan 35. The discharge chute 36 on the other hand is locatedto the right of (as viewed in FIG. 2) and downwardly of the inlet to theactive return line.

Flow through the active return line 37 is controlled by a valve 40 whichis part of the automated rinse/valve assembly 26 (alternatively, amanually operated valve may replace the automated valve assembly 26). Apassive return line 41 is coupled to the settling box 15 and has itsdischarge end leading into the process tank 21. The connection of thesettling box passive return line 41 to the settling box 15 is at anelevation above the bottom of the settling box so that fine solidspassing through the wire mesh fine screen 12 are detained, allowing themto settle in the settling box 15 with only a relatively small amount ofthem being returned through the passive return line 41 to the processtank 21.

The process tank or sediment basin 21 will vary in size andconfiguration from application to application; however, the function ofthe pump suction line 30 and the sparger return line 31 are functionallythe same in those applications. Inlets to the suction line 30 arelocated at spaced locations on the bottom of the process tank 21.Similarly, the sparger return line 31 has a number of outlets on thebottom of the process tank at spaced locations spaced away from theinlets of the suction line.

Perspective view FIG. 1 shows the apparatus 10 in a conditionunconnected to the process tank 21. The apparatus 10 is mobile and isprovided with casters 60 so that it can be easily relocated andhydraulically connected to different process tanks 21. Alternatively,the apparatus 10 may be provided without casters and mounted securely atthe stand base. FIG. 9 is a perspective view of the cart 33 or standupon which the elements of the apparatus are mounted.

Referring to FIGS. 6 and 7, the wedge wire coarse screen 11 isillustrated. FIG. 10 is a perspective detail view of the separation pan35 within which the coarse screen 11 is mounted with the screen beingsupported on the upper screen support 61 and lower screen support 62.FIG. 1 shows a lid 63 for the separation pan 35 which prevents splashingto the outside of the apparatus. The coarse screen 11 is a commerciallyavailable item and may be obtained, for example, from Johnson Screens inNew Brighton, Minn., specifying the wire size, spacing and cant.Referring to FIG. 6, the spacing dimension 65 is the distance betweenthe individual wires 66 of the screen. The cant angle 67 is formedbetween the top plane of the wedge wires 66 and a plane parallel to theribs 70 upon which the wires 66 are attached. As can be seen in FIG. 6,the wires 66 have a triangular cross section (hence the term “wedge wirescreen”). In a preferred embodiment of the invention, the dimension 65for the coarse screen 11 is nominally 200 micron and the cant angle 67is 5 degrees. In comparison, the fine screen 12 has a nominal dimensionbetween its wires in the same preferred embodiment of 100 micron. FIG. 8is a perspective view of the fine screen 12 which is received withinsettling box 15 and has a lip 71 allowing it to rest upon the top edgeof settling box with the fine screen 12 in spaced relation to the insideof the settling box 15. The settling box 15 has a silt rinse line 54controlled by a suitable valve 56.

As further shown in FIG. 5, an assembly which includes the pumpdischarge line 24, 24A and 24B is the pipe riser/support assembly 28which has the dual function of supporting the separation pan 35 andconveying fluid to the head compartment 32 of the separation pan 35.Thus the portions of the pump discharge line 24, which are the pipes 24Aand 24B, are rigid and fixed to the rigid cart or stand 33 as well asthe head compartment 32 of the separation pan 35, thereby supporting theseparation pan.

The apparatus functions in four (4) basic modes of operation: 1) NormalOperation Mode, 2) Screen Rinse Mode, 3) Maintenance Mode, and 4) TankRefresh Mode.

During normal operation, process fluid and suspended solids areconducted from the process tank or sedimentation basin 21 via acustom-designed suction manifold. Hydraulic elevation head within thetank, along with assistance from the self-priming trash pump, providethe motive energy required to maintain fluid flow through the separator.On the discharge side of the pump, the fluid flow is split with one ofthe branches returning fluid directly back to the tank via the spargingreturn line 31 and the other directing the fluid through thevertically-oriented pipe riser/support assembly 24, 24A and 24B thatfeeds the head compartment 32 of the separation pan 35. The spargingline 31 directs relatively high-pressure fluid to the bottom of theprocess tank to continually stir and suspend settled solids for enhancedpick-up by the suction manifold. The pump also delivers fluid to thehead compartment 32 of the separator pan 35. Upon filling the volume ofthe head compartment 32, the fluid then passes through a rectangularopening, and down across the coarse screen 11 under gravity.

Upon contacting the wedge wire screen 11, the contacting fluid issheared away to the underside of the screen, leaving appreciable solidloading on top of the screen. In FIG. 6, arrows 74 represent the flow offluid that is sheared away from the main flow represented by arrows 75.Fluid on the underside of the screen falls and travels down the bed ofthe separation pan 35 and passes across the quaternary separationelement (magnet(s) 16). The magnets attract and hold essentially allfine ferromagnetic material that may have passed through the primaryseparation element (the magnets are an option). The fluid flows back tothe process tank under gravity via the active return line 37 connectedto the bottom underside of the separation pan. Continual operation innormal mode reduces solid content in the process fluid and resultantlyleaves relatively large-sized solids accumulating on the top side of thewedge wire screen and finer ferromagnetic material on the magnet. Hence,primary and quaternary separation are achieved.

In time, accumulating solids on the top of the wedge wire screen willautomatically propel down the face of the wedge wire screen 11 under theinfluence of gravity and eventually drop through the discharge chute andinto the strainer basket 12. In some applications, accumulating debrison the wedge wire screen builds without readily releasing under theinfluence of gravity alone. The result is continual enlargement of thesolids pile on the wedge wire screen until the solids begin interferingwith the fluid being sheared near the upper portion of the wedge wirescreen. The damming that manifests is often sufficient to continueautomatically pushing solids slowly down the face of the screen. Inapplications where debris appreciably and undesirably “hangs up” on thewedge wire screen without being adequately released under gravity anddamming, a simple rinse cycle may be initiated which removes virtuallyall loose solid debris from the wedge wire screen.

By way of adjustable timers within the pump/screen rinse controller 25,the rinse valve 40 in the active return line 37 automatically closes ona periodic basis for a short preset duration. In closing the valve,fluid flow is obstructed from returning to the process tank. Under thiscondition, with the pump continually feeding fluid to the separationpan, air beneath the wedge wire screen in the separation pan 35 becomespressurized which severely limits fluid flow through the wedge wirescreen; therefore, the fluid instead, flows down across the entirelength of the screen, which vigorously and quickly rinses debris off thescreen and into the strainer basket 12. Upon opening the rinse valve,fluid is again returned to the process tank and normal operation moderesumes. As a consequence of releasing both solids and liquid into thestrainer basket 12 during a screen rinse cycle, secondary, tertiary andquaternary separation processes commence. In the strainer basket, thesecondary separation element (fine woven-wire mesh screen) arrests largeand moderately sized solids and passes fluid and small fines to the openannular space between the outside of the strainer basket and settlingbox. In the settling box, the fluid must elevate to the level of theoutlet before passively returning fluid back to the process tank. Thedetention time inherent in the settling box permits fine settleablesolids to accumulate in the bottom of the settling box. Virtually allfine suspended ferromagnetic material passively returning to the processtank are attracted to a magnet 17 within. The rate of fine filtrationdepends on the frequency of the screen rinse cycle. The frequency isadjusted to fall within the hydraulic capacity of the strainer basketand settling box.

By closing the rinse valve, the rinse is initiated because the coarsescreen hydraulic capacity temporarily drops to near zero, so that flowthrough the separator is in excess of screen capacity. Essentially, thesame condition may result by increasing supply flow for a short durationin excess of screen capacity, for example by increasing pump speed oradjustment of a throttling valve on the supply side of the coarsescreen.

FIGS. 3 and 4 show some disassembled elements taken in the maintenancemode of the apparatus. Depending on the particular application, the finescreen 12 will become filled with solid material and need emptying. FIG.4 particularly shows this mode of the process. Also shown in FIG. 4 arethe magnets 16 and 17 removed from their mountings in the apparatus.Preferably, these magnets include non-magnetic end portions tofacilitate removal of the ferromagnetic material from the magnets. Inmaintenance mode, the bottom of the settling box 15 may be cleaned ofsettled solids by flushing through the settling box drain line 54 and byappropriate manual tools.

Flat-bottomed tanks are inherently difficult to filter when solidswithin are moderately to highly settleable. The present inventionaddresses the challenge associated with attempting to filter industrialfluids within flat bottomed tanks where the solids characteristically donot concentrate, but rather, spread across the bottom surface of thetank and/or suspend within the process fluid.

To capture settleable and suspended solids, the suction manifold isprovided with several hydraulic pick-ups located at spaced locationsalong the bottom of the tank. The piping network is designed withsplit-cut open pipe ends (not shown) and sweep fittings (not shown) forenhanced hydraulic efficiency. The suction manifold is easily assembledand disassembled with union fittings. Pipe sizes of the suction manifoldare chosen to prevent pump cavitation. Pipe materials are selected tominimize corrosion and threaded connections are made only moderatelytight and without sealant to ease assembly and disassembly. The suctionmanifold is arranged to avoid interference with existing equipmentwithin the process tank. The suction manifold piping layout isdetermined in attempting to minimize the number of fittings. Dependingon the application, all or most of the manifold may be pre-cut andassembled into a kit. Cam-lok fittings and heat resistant rubber hoseare preferably used in the suction line 30 in interconnecting the tankto the suction port on the pump 23. Many applications use heated fluidsthat may approach boiling temperatures, so materials resistant to heatare imperative. Material selection of the cam-lok fittings is made basedon cost and corrosion resistance. Hard piping may replace hose andcam-lok fittings. Cam-lok fittings and hose are chosen to easeinstallation and provide flexibility in moving the apparatus.

Process tank penetrations for all line interconnections areprefabricated from full couplings and mounting plates. The mountingplates assure a water-tight seal and enlarge the mounting area forstress-reduction. The standard pump 23 is a self-priming centrifugaltrash pump. The self-priming feature allows the unit to work on tanks inwhich the suction head on the pump is low. A trash pump is preferable asrelatively large infrequent objects are likely to pass without damagingthe pump. A clean out port on the trash pump allows easy access todebris that may accumulate within the pump housing. The pump is selectedwith mounting feet that fit conveniently across closely spaced pumpmount rails of the stand base 33 for maintaining a relatively smallfootprint. The pump drive motor is close coupled for compactness ofdesign. The drive motor housing is finned for readily transferring heatand/or offset slightly through an extended shaft. The pump drive motoris oriented toward the inside of the stand for protection. Alternativepump seals are available having higher heat and chemical resistance. Thepump drive motor is TFFC (and oversized in hydraulic capacity to supportthe sparging manifold connected to the discharge of the pump. The checkvalve in the pump is removed to drain the riser/support assembly 24whenever the pump shuts off.

Pressurized fluid flows through the sparger discharge line 31 to theprocess tank. The sparging manifold is fanned out to nozzles that sprayand stir the bottom of the process tank; ultimately encouraging settledparticles to the suction points on the suction manifold. A valve 45 onthe sparger discharge line 31 is used to throttle sparger flow andbalance discharge flow to the head compartment 32 of the separation pan35. In the event debris obstructs the sparger line, the connections ofthe suction and sparger line at the pump or process tank may be brieflyswitched with the isolation valve on the original suction manifoldclosed which ultimately directs fluid backwards through the spargerline, dislodging the obstructing debris and shooting it vertically upthrough the pipe riser/support assembly to the head compartment 32 forultimate release. The suction and sparger line sizes are selected tominimize obstruction. Once cleared, the suction and sparger lines arereconnected in their normal configuration with normal valve throttlesettings re-established.

A thermal dispersion flow switch mounted to the pump discharge senseswhether or not there is adequate flow through the pump. In the eventadequate flow is not established in a preset time period, the pump willshut off and signal a visible alarm light on the face of the pump/screenrinse controller 25. Initial pump priming is easily established byremoving the cam-lok fitting and pouring fluid down into the dischargeport. Also, the process tank should be checked for fluid and theisolation valve should be in the full open position. After establishingprime and open connection to fluid within the process tank, the alarmlight is pushed for resetting and the pump run button is pushed forrestarting.

A throttle valve 46 in the pump discharge line 24 is adjusted toregulate flow to the head compartment 32 of the separation pan 35. Theconnection between the head compartment throttling valve 46 and the piperiser/support assembly 28 is made with flexible hose and cam-lokfittings for relief in adjusting the horizontal and vertical position ofthe pipe riser/support assembly. As the name implies, the piperiser/support assembly is dual purpose, offering structural columnsupport of the separation pan and hydraulic conveyance of theliquid/solid mixture being separated by the apparatus. In the presentdesign, the two vertical pipes 24A and 24B (because of their relativelysmall diameter to flow rate ratio) maintain adequate velocity and advectthe solids all the way to the primary separation element 11 withoutreversing direction. The material of the pipe riser support assembly isselected to resist corrosion. The pipe riser/support assembly isanchored at four symmetrically aligned locations to the stand 33 of FIG.9. In anchoring the assembly, vertical and horizontal adjustment is easywith sliding the clamps and pipes horizontally along the strut forhorizontal adjustment and sliding the pipes vertically within the clampsfor vertical adjustment. The separation pan is quickly and easilyremoved by loosening the hydraulic unions just beneath the upper headcompartment 32 of the separation pan 35.

The invention operates with both elevation head and velocity head. Thefluid pressure generated by the pump is totally converted to velocityhead as fluid escapes from the head compartment 32 to the coarse screen11. The resultant velocity supports the shearing action of fluid on thewedge wire screen face. As remaining fluid proceeds down the face of thescreen, elevation head is converted to velocity head, which furthersupports the shearing action of the fluid on the screen face. Duringconditions of relatively low flow to moderate flow, contribution fromall three energy components drives the separation. For relatively highto extremely high flows, a deflector plate 50 on the upper headcompartment cover directs flow down against the screen to enhance theseparation of liquid from solid. The fluid energy is not increased bythe deflector plate, rather, the deflector plate optimally orients thevelocity energy component in a favorable direction to ultimately achievegreater wedge wire screen shearing capacity.

Downward along the wedge wire screen face, the fluid follows a profileof decreasing discharge through the screen pores until all the fluid haspassed across the screen face. Typically, the fluid is removed from thesolid across the first half of the screen length, leaving the secondhalf for accumulation of solids. The biting/shearing action of the wateragainst the wire edges over the first half of the screen length assiststhe passage of fluid, yet the same biting action undesirably inhibitsthe release of solids down the second half of the screen face resultingin solids accumulation at the shearing edges of the screen wires.

FIG. 11 shows a new wedge wire screen design where the cant angle on thescreen wires transitions in step-wise fashion from having high shearcapacity at the upper region 80 of the screen to essentially none at thetoe region 81 of the screen. In this way the fluid is removed at thebeginning of the flow path where the screen wires have greater tiltangle, whereas near the toe of the wedge wire screen, the solids slidedownward more readily with the screen wires forming a fairly lowfriction plane. In the illustrated example, there are three cant anglesin the regions 80, 81 and 82. In this design, as another example, thelength of wedge wire screen is divided into 6 fairly equal lengthregions, where each region has a set of wires with equal cant, 5-degreecant in the first region, 4-degree cant in the second, 3-degree cant inthe third, 2-degree cant in the fourth, 1-degree cant in the fifth and0-degree cant in the sixth. Also, another way of encouraging the solidsto slide down the lower portion of the screen would be to transitionwire spacing from relatively large opening at the top of the screen,decreasing to near zero at the toe of the screen.

The wedge wire screen is easily inserted within a slot of the upperscreen support 61 (FIG. 10). The screen fits within the separation panwithout fasteners. The screen is removed and replaced by hand for easinginstallation and maintenance with no specialty tools required. Thescreen is adapted at the toe with a plate 77 that forms a smoothtransition off the last wedge wire to enhance the release and propulsionof solids from the wedge wire screen.

Fluid moves down the separation pan 35 to the lower portion of theseparation pan where the magnets 16 attract ferromagnetic material. Inone preferred embodiment, fluid filling the lower portion of theseparation pan provides sufficient elevation head for a flow rate ofapproximately 35 gpm before the level in the lower separator panoverflows the upper edge of the lower screen support. The fluidcontinues predominately flowing through the coupling mounted on theunderside of the lower separator pan and through valve 40. The fluidreturns to the process tank 21 through the active return line 37.

The pump/screen rinse controller 25 initiates a screen rinse eitherautomatically or by manual push button. Alternatively, a manuallyoperated valve may be actuated to achieve the same screen rinsingeffect. In any case, upon initiation of a screen rinse, sheet flowcommences down the face of the screen which dislodges accumulatedsolids. As a consequence, liquid and solids slide down off the toe ofthe screen and continue down across the top of the lower screen supportuntil falling vertically through the liquid/solid discharge chute 36 tothe strainer basket 12. The strainer basket fits within the settling box15. The lip 71 of the strainer basket fits flush and level on the topedges of the settling box to create pressure differential across thestrainer basket for improved motive in driving fluid across the finescreen material of the strainer basket. Passive fluid flow returning tothe process tank through line 41 creates slight negative pressure withinthe annular space between the strainer basket and the settling box whenflow across the screen is temporarily and lightly obstructed. Under thiscondition, atmospheric pressure assists in driving the fluid across thefine screen to the low pressure region on the other side of the finescreen, leaving most of the solids within the basket. Most of the smallfines that flow unimpeded through the basket screen will settle in thesettling box or be attracted to magnet 17 within. Magnet 17, as well as16, are held in place with spring clips (FIG. 10). The clips are locatedalong the magnet to avoid interfering with the attracted ferromagneticmaterial when the magnet is removed for cleaning. Fluid flowing out ofthe settling box must achieve the level of settling box outlet. Thisdrives the detention time required for settling. Periodically, theinternal strainer basket is removed to dispose the accumulated solidswithin. A cam claw latch (not shown) on one side of the settling box isreleased, allowing the top of the strainer basket/settling box assemblyto rotate away from the stand about the bottom hinge as shown in FIGS. 3and 4. With the strainer basket/settling box assembly rotated away, thebasket and magnets within are easily removed for maintenance.

If installed as an option, a proximity switch against the settling boxautomatically interrupts electrical power to the pump when the settlingbox is rotated away from the stand. In this way, an automaticallyprogrammed screen rinse cycle will not be initiated with the strainerbasket/settling box rotated out of the way, thus preventing fluid anddebris from discharging uncontained. A chain 55 (FIGS. 1, 3 and 4)limits the settling box rotation and is welded at one end to the side ofthe settling box and bolted at the other end to the stand. The chain islocated on the opposite side of the settling box to which the cam clawlatch is fastened thereby avoiding interference.

The strainer basket is hung from the top lip 71, thus allowing freespace and increased settling volume directly beneath the bottom surfaceof the strainer basket. The internal strainer basket is removed bypulling up on the centrally located handle 85 near the top of thestrainer basket. The inverted V-shape of the handle sheds fluid andsolids that are discharged while providing structural integrity to thestrainer basket. Removed from the settling box, the strainer basket isinverted and lightly tapped against a receptacle to remove and disposeof solids within. Spray water from a garden hose and pressurized air mayalso be used to rinse the basket and dislodge collected solids.

The inside bottom of the settling box will have fine sediments that areeasily washed away by jetting action of a spray hose with the rinse linevalve 56 open. The silt rinse line may feed a 5-gal. bucket or existingfloor drainage. After cleaning, the strainer basket and magnet arereplaced and the settling box/strainer basket assembly is lightlyslammed shut and automatically retained by the cam claw latch. Thepassive return line 41 length is cut in slight excess to provide slackwhen rotating the settling box away from the stand. Alternatively, acoiling hose arrangement spiraling downward in the direction of passivereturn optimizes gravity return assistance.

In dumping a process tank 21, the fluid can be pumped through theapparatus and then drained directly to waste, instead of flowing backthrough the active return line. This will separate the solids from theliquid while draining the process tank. When the process tank iscompletely drained via the pump, the flow switch will sense a no-flowcondition and turn off the recirculating pump. In releasing fluid fromthe process tank this way, the discharged wastewater is not undulyloaded with solids, thereby reducing downstream waste treatment costs.The controller may be equipped with a push-button that may be usedfor: 1) partial periodic process tank purging or, 2) full and completeprocess tank draining. With this releasing feature, the separator may beused for filtering to waste, whether fluid is purged or completelydrained from the process tank. Partial periodic draining systems may berefreshed with make-up water on level control signals from the processtank.

The settling box fastens to the stand through solid strut with springnuts. The strut/nut fastening system allows horizontal adjustability andremoves the high tolerance hole mating required in conventionalfastening systems. The settling box must be rotated away from the standto remove or reinstall the strainer basket (as shown in FIG. 4).

The pump/screen rinse controller 25 provides ON/OFF control of therecirculating pump and ON/OFF control of the screen rinse function. Thecontroller is enclosed in an electrical enclosure with adequateelectrical rating. The pump is manually started by pushing a greenpush-button that illuminates when the pump is running. The pump ismanually stopped by pushing a red push-button. The screen rinse functionmay be activated either manually or automatically on a time basis. Thescreen rinse function is selected by turning a selector switch to theENABLE position. A screen rinse is initiated by momentarily pushing theblue push-button in. The blue light of the push button will illuminateduring the screen rinse and not illuminate when the timed screen rinseterminates. The screen rinse is also on an automatic timer that willinitiate at preset intervals. Both the frequency and duration of thescreen rinse cycles are adjustable via timers located within thecontroller enclosure. Frequency and duration are determined by thehydraulic capacity of the strainer basket along with the desiredfiltration rate across the fine screen of the strainer basket. The pumpwill not run continuously if the flow switch does not sense flow,thereby preventing damage from running the pump dry. The flow sensor isequipped with an adjustable timer that turns the pump OFF after thepreset time period to prevent damaging the pump in running dry for toolong. Also, an optional proximity switch associated with the strainerbasket/settling box will immediately prevent the pump from running, ifthe settling box is rotated away from the stand. Whether by low flow orby having the proximity switch tripped, the yellow NO-FLOW alarm lightwill illuminate. After correcting the tripping condition, the yellowlight is pushed in to reset the system and then the pump may be turnedon. When screen rinsing is not desired, the screen rinse selector switchis turned to the DISABLE position. A drain feature may be added to thecontroller that opens a second valve on a drain line. The drain turnsoff automatically after the tank is pumped dry and the recirculationpump turns off via the flow switch.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected. One modification that might bemade would be incorporating the invention as a part of a manufacturingline (or specific equipment within that line). In such an alternative,the controls would likely be a part of the manufacturing line. Anotheralternative embodiment might include the rinsing process above describedbut would not include a recirculation line.

1. A process for separating solids from liquids, comprising: providing asupply of a solid containing liquid; providing a first screen arrangedat an angle to the horizontal and having an upper end and a lower end;providing an active return line positioned below said first screen toreceive liquid that flows through said screen and to return the liquidto the supply; conveying the solid containing liquid from said supply tosaid first screen to filter the solid containing liquid; providing apump to supply the supply of solid containing liquid; increasing a speedof the pump to thereby increase the flow of liquid wherein the liquidrinses an upper surface of the screen and causes solids thereon to moveoff the screen.
 2. A process for separating solids from liquidscomprising: providing a supply of a solid containing liquid; providing afirst screen arranged at an angle to the horizontal and having an upperend and lower end, said upper end receiving the supply of solidcontaining liquid; providing a throttling valve on a supply side of thescreen; providing an active return line positioned below the firstscreen to receive liquid that flows through the screen and to return theliquid to the supply; conveying the solid containing liquid from thesupply to the screen to filter the solid containing liquid; andcontrolling the throttling valve to increase the supply of solidcontaining liquid wherein the upper surface of the screen is rinsedcausing solids thereon to move off the screen.